Very-high-rate Digital Subscriber Line 2 (VDSL2), a new transmission standard proposed by the ITU-T (International Telecommunication Union-Telecommunication sector) in July 2005, is completely based on Discrete Multiple Tone Line Coding (DMT) technology. VDSL2 not only has a long-distance transmission capability as Asymmetric Digital Subscriber Line 2+ (ADSL2+), but also increases data transmission rate of VDSL from 70M bps (downlink)/30M bps (uplink) to 100M bps (downlink)/100M bps (uplink). VDSL2 combines higher access rate, better Quality of Service (QoS) control and long-distance transmission capability similar to that of ADSL, and soon becomes the focus of new generation access technology.
Operators incline to utilize new technologies, but do not want to upgrade equipment before recovering prior investments. Operators hope to use existing Customer Premises Equipment (CPE), e.g., ADSL2+ modem, when the new VDSL2 technology is employed in access equipment, which leads to stricter requirements for access equipment.
DSL physical layer chips on user boards of the existing Digital Subscriber Line Access Multiplexer (DSLAM) are designed in consideration of compatibility, and are able to support both ADSL2+ and VDSL2 accesses. However, in order to achieve full ADSL2 and VDSL2 compatibility, DSLAM protocol also should be modified adaptively.
As shown in FIG. 1, a user board of a DSLAM device in the prior art includes a DSL physical layer chip, a protocol processing chip and an uplink interface chip. The DLS physical layer chip functions as an interface to network transmission devices, e.g., twisted pairs. The uplink interface chip functions as an interface to subscriber terminal devices. Traffics are transmitted on the twisted pair in data frames, and the traffics processed by the subscriber terminal devices should be in cells, thus the protocol processing chip is used to convert data frames into cells and/or convert cells into data frames. Multiple techniques can be used for the protocol processing.
The first technique used for the protocol processing is Asynchronous Transfer Mode (ATM). The protocol processing chip and the DSL physical layer employ a Universal Test & Operations PHY Interface for Asynchronous Transfer Mode (UTOPIA) to transmit standard ATM cells. The standard ATM cells carry Asynchronous Transfer Mode Adaptation Layer 5 (AAL5) frames. At present the most widely used DSL technologies of the ADSL family, e.g., ADSL, ADSL2 and ADSL2+, all employ this mode. However, ATM can only be used to transmit standard ATM cells, and is thus not suitable to the VDSL technology.
The second technique used for the protocol processing is Packet Transfer Mode (PTM). The protocol processing chip and the DSL physical layer generally employ a Strand Medium Independent Interface (SMII), Medium Independent Interface (MII), or Packet over SONET (POS) interface to transmit High Level Data Link Control (HDLC) frames, Ethernet in the First Mile (EFM) frames, layer-2 or layer 3 packets given by the DSL physical layer by decapsulating the HDLC or EFM frames. Incompatible with the UTOPIA, PTM is suitable for handling HDLC or EFM frames only, thus the PTM is suitable for the DSL technologies of the VDSL family, e.g., VDSL, VDSL2 and VDSL2+, but not for the DSL technologies of the ADSL family.
In order to support both ADSL and VDSL accesses, the protocol processing chip on DSLAM user board should be able to process both standard ATM cells and PTM packets. However, in the prior art standard ATM cells and PTM messages cannot be processed by a same device, thus cannot support both the ADSL family and the VDSL family.